1. Field of the Invention
This invention relates to electronically variable large-information-content displays, and more particularly relates to displays featuring a novel image plane translator as a face plate or substrate which transfers subpixel beamlets from the translator's inner surface to its outer surface without divergence.
2. Summary of Prior Art
In the manufacturing of display devices based on cathode ray tube, liquid crystal display, field emission display, and thin film electroluminescence (CRT, LCD, FED and TFEL) technologies, the glass face plate plays a major role as a substrate. The light emitting pixels are on the inner surface of the face plate and the image is viewed by the observer on the other side. Each pixel (i.e., picture element) which may be thought of as a unitary dot of appropriate color combination, is made up of several subpixels which, when mixed by the human eye, provide the color to be sensed. Subpixels of red, green and blue in various combinations provide a full color capability to the pixel. The face plate must be thick enough to provide sufficient mechanical strength, and should have acceptable thermal, optical, vacuum-seal, and chemical properties in order to deliver good image quality with low manufacturing cost. For purposes of this discussion, the subpixel is an individual spot of light of a primary color. Normally, three subpixels (red, green and blue--R, G, B) are grouped as a three-subpixel basic pattern unit. In a display for human eyes, the pattern unit is integrated by the human eye and brain as one full-color pattern pixel.
In displays viewed directly by the human eye, the thickness of the display face plate does not cause image degradation because the eye images each pixel through the thickness of the face plate directly on the retina. There are, however, numerous situations in which the image as generated on the inner surface of the face plate is not viewed directly; instead, further processing of the image (such as translation or modulation) is required on a subpixel-by-subpixel basis. That is, the individual beamlets of light generated from all subpixels on the face-plate inner surface must be transmitted accurately to another image plane (in a receiving device) for further processing. Clearly, in a conventional display that uses a conventional face plate, the thickness of the face plate may make such further processing impossible, since radiation from the subpixels diverges within the face plate, prior to being supplied to the receiving device for further processing. Overlap between rays from adjacent pixels reaching the receiving surface may be so great that individual pixels can no longer be resolved.
The problem of pixel-wise transferring an image from one plane to another is solved by using an image plane translator (IPT) as a face plate. An IPT transfers the subpixel beamlets from its inner surface to its outer surface without expansion by divergence. This has the effect of making the face plate appear as through it has zero thickness. The conventional IPT, although expensive, has become a frequently-used solution for tandem light processing systems which require image transfer through glass without divergence of the subpixel beamlets.
The construction of prior-art IPTs is based on fiber-optic technology. A fiber-optic IPT is essentially a fused bundle of short optical fibers. Each optical fiber extends from the inner surface to the outer surface of the composite face plate, forming interference-free light pipes--one per pixel (or subpixel)--to carry each pixel through to the outer surface without spreading to adjacent pixels. Manufacturing processes for such IPT plates made of a large number of fused optical fibers are very complex, leading to very high-cost plates (nearly $10,000/plate for a 25 cm diagonal display). Consequently, the use of such IPT plates is limited to only a few display applications, generally quite small in area, where the overall system cost is high (so that the IPT cost is only a small fraction of the total system cost).
There is, therefore, a great need for an inexpensive high-quality IPT which can be used as a substrate for high-quality large displays. That is, there is a need for an IPT that is big enough, strong enough and inexpensive enough to be used as the face plate in a wide variety of displays and other applications where pixel-wise transposition of the image from an inner surface to an outer surface is required or desirable.